Syringes fitted with means to retract automatically the needle at the end of the injection are known.
One of these syringes is shown in Edward F. Allard, U.S. Pat. No. 4,838,869, which is related to a hypodermic needle which retracts into the body of the syringe after use, thereby preventing the reuse and the spread of diseases normally associated therewith. This syringe comprises outer and inner cylinders wherein the outer cylinder has a first end with a first opening for effecting the protusion of said needle and a second end with a second opening allowing for the moving of the inner cylinder through the outer cylinder. The inner cylinder is located within the confines of the outer cylinder for receiving and storing the needle when retracted.
Plunger means are in slidable contact with the inner wall of the outer cylinder for effecting a vacuum inside the syringe upon actuating the plunger in an outward direction, whereby a fluid may be drawn into the outer cylinder and expelled upon actuating the plunger inwardly.
The needle which extends through the second opening of the outer cylinder has a head somewhat larger than the diameter of the needle to establish a rim that can be used to firmly hold the needle in place during use by holding tabs within the first end of the outer cylinder; the needle is spring loaded, whereby upon contacting the holding tabs with the end of the plunger the spring loaded needle is caused to be disengaged and retracted into the inner cylinder for storage.
The problems which the syringe device shown in U.S. Pat. No. 4,838,869 does not solve are the following:
1--To allow the syringe to be completely emptied out.
2--To shear the closing element placed in the opening of the second cylinder housed by the first cylinder.
3--To prevent the needle from being easy reached after use of the syringe.
4--To place sealing means at a suitable position in order to prevent the fluid to be injected from being transferred into a cavity which houses the head of the needle.
5--To properly dispose the needle with respect to the outer cylinder.
6--To allow the inner cylinder to be clamped by the outer cylinder in order to prevent the needle from being easy reached after use of the syringe.